A heat pump is a machine or device that transfers thermal energy from one location, at a lower temperature, to another location, which is at a higher temperature. Accordingly, heat pumps move thermal energy in a direction opposite to the direction that it normally flows. Some types of heat pumps are dedicated to cooling only, some types are dedicated to heating only, and some types perform both functions, for instance, depending on whether heating or cooling is needed at the time. Heat pump HVAC units have been used for some time to heat and cool spaces that people occupy such as the interior of buildings. Heat pumps have also been used for other purposes such as heating water. Heat pumps are typically more efficient than alternative heat sources, such as electrical resistance heating, because heat pumps extract heat from another source, such as the environment, in addition to providing heat produced from the consumption of electrical power. Further, in some situations, the heating and the cooling are both put to beneficial use at the same time, such as heating domestic hot water while cooling air for air conditioning. As a result, heat pumps often reduce energy consumption in comparison with other alternatives.
Heat pumps have been used that heat and cool an enclosed space within a building and that also heat domestic hot water. A problem encountered with such systems, however, is that an appropriate refrigerant charge for one mode of operation has been inappropriate (i.e., insufficient refrigerant charge or excessive refrigerant charge) in another mode of operation. For example, during conditions under which a particular heat exchanger of the heat pump is not needed for transferring heat, liquid refrigerant has accumulated in that heat exchanger reducing the available charge for the system to an inappropriately low level of charge. This has occurred, for example, during conditions under which the outdoor heat exchanger is not needed for transferring heat, while the water is being heated and the space is being cooled. This has also occurred, as another example, during conditions under which the indoor heat exchanger is not needed for transferring heat, while the water is being heated and heat is being extracted from the outdoor air. In the past, it was necessary to correct or compensate for these inappropriate refrigerant charge levels in different modes of operation with complex and expensive refrigerant charge management hardware and systems, or else it was necessary to avoid certain modes of operation such as those modes just mentioned, or the heat pumps operated substantially less efficiently during such modes of operation.
Further, U.S. Pat. No. 4,299,098 (Derosier) describes controlling refrigerant charge in a heat pump water heater by venting an inactive heat exchanger to the suction side of the compressor. The heat pump of Derosier, however, is not able to heat the space and heat water at the same time, and is not able to heat water while also rejecting heat to the environment while the space is being cooled. In addition, the heat pump of Derosier requires many expensive components, including control valves and check valves.
As a result, needs or potential for benefit or improvement exist for refrigerant charge management methods and systems for heat pumps that also heat water that are less expensive, that utilize existing components to a greater extent, that provide for more modes of operation of the heat pump, that increase the efficiency of the heat pump, at least during particular modes of operation, that are less complex, that can be readily manufactured, that are easy to install, that are reliable, that have a long life, that are compact, that can withstand extreme environmental conditions, or a combination thereof, as examples. Further, needs or potential for benefit or improvement exist for methods of controlling, manufacturing, and distributing such heat pumps, HVAC units, buildings, systems, devices, and apparatuses. Other needs or potential for benefit or improvement may also be described herein or known in the HVAC, domestic hot water heater, or heat pump industries, for example. Room for improvement exists over the prior art in these and other areas that may be apparent to a person of ordinary skill in the art having studied this document.
Further background information describing certain aspects of prior art and problems therein includes U.S. Pat. No. 5,140,827, issued to Wayne R. Reedy on Aug. 25, 1992. Potential for benefit exists over the prior art including managing refrigerant charge with fewer components, less expensively, more reliably, or a combination thereof.
These drawings illustrate, among other things, examples of certain aspects of particular embodiments of the invention. Other embodiments may differ. For example, in some embodiments, components or acts may be omitted, or acts may be performed in a different order. Various embodiments may include aspects shown in the drawings, described in the specification, shown or described in other documents that are incorporated by reference, known in the art, or a combination thereof, as examples.